Plum blossom couplings (also known as jaw couplings, spider couplings, or ML/LM series couplings) are among the most versatile and widely used flexible couplings in industrial power transmission. With a simple three-piece design – two metal hubs and an elastomeric spider – they offer an excellent balance of torque capacity, misalignment compensation, and shock absorption.

This guide explains how plum blossom couplings work, their key advantages, and how to select the right ML model for your application.

1. What Is a Plum Blossom Coupling?

A plum blossom coupling (jaw coupling) consists of:

• Two metal hubs – with identical protruding claws

• A plum-shaped polyurethane spider – placed between the hubs

The spider transmits torque while absorbing shock, dampening vibration, and compensating for misalignment. The plum blossom shape of the elastomer gives the coupling its name. This design provides zero backlash operation when properly preloaded, making it suitable for applications requiring precise positioning.

💡 Plum blossom couplings are widely used in applications with frequent starting, reversing, and medium-speed, medium-torque requirements.

2. Key Advantages of Plum Blossom Couplings

3. How to Select the Right ML Model

Step 1: Determine Your Torque Requirement

• Calculate the torque your application requires.

• Select a model with rated torque ≥ 1.5× your requirement.

• ML series covers 16–5600 N·m.

Step 2: Match Shaft Diameters

• Measure your shaft diameters.

• Select a model with a bore range that accommodates your shafts (6–160 mm).

• H7 bore tolerance is recommended for precision fit.

Step 3: Consider Speed Requirements

• Verify the coupling’s maximum speed exceeds your operating speed.

• ML series offers speeds up to 15300 RPM.

Step 4: Consider Space Constraints

• Measure available space for the coupling (outer diameter and length).

• ML series offers compact sizes for space-constrained installations.

Step 5: Evaluate Operating Conditions

• Temperature: -35°C to +80°C – verify your operating range.

• Environment: Dusty, wet, or corrosive – consider material options.

• Start/Stop frequency: ML couplings are suitable for frequent starting and reversing.

Step 6: Select Spider Hardness

• Standard: 95-98 Shore A for most applications.

• Softer spiders offer better damping; harder spiders offer higher torque capacity.

4. Applications Where ML Couplings Excel

5. Polyurethane Spider – The Heart of the Coupling

The polyurethane spider is the critical component that determines coupling performance:

💡 The spider is the wear element – designed for easy and cost-effective replacement without moving the hubs or disconnecting the shafts.

6. GB/T5272-2002 Standard – Quality Assured

The ML coupling is manufactured to GB/T5272-2002 (replacing GB5272-85), which ensures:

• Consistent quality – standardized dimensions and tolerances

• Interchangeability – compatible with other LM/ML series couplings

• Reliable performance – tested and proven design

• Global acceptance – recognized standard worldwide

7. Real‑World Example – Mining Conveyor Upgrade

A mining company was experiencing frequent coupling failures on heavy-duty conveyors. The existing couplings required regular lubrication and failed prematurely due to shock loads and misalignment.

They switched to Apex Coupling ML plum blossom couplings (45# steel hubs, polyurethane spider, maintenance-free). Results:

• Service life extended – polyurethane spider withstood shock loads

• Maintenance eliminated – no lubrication required

• Downtime reduced – quick spider replacement without moving hubs

• Shock absorption improved – polyurethane spider protected connected equipment

8. Installation & Maintenance Tips

1. Clean shafts and bores – Remove oil, grease, and debris before assembly.

2. Check alignment – Even with misalignment compensation, keep within recommended limits.

3. Install hubs – Mount the hubs on the driving and driven shafts.

4. Install spider – Insert the polyurethane spider between the hubs.

5. No lubrication required – Coupling is maintenance-free.

6. Inspect spider periodically – Check for wear, cracking, or deformation.

7. Replace spider – When worn, replace without moving hubs.

9. Selection Checklist

• □ 

  Model: ML1 to ML12 – select based on torque and bore requirements

• □ 

  Hub material: 45# steel, cast iron, ductile iron, or stainless steel

• □ 

  Spider material: Polyurethane – oil & wear resistant, maintenance-free

• □ 

  Spider hardness: 95-98 Shore A – standard for most applications

• □ 

  Bore: H7 tolerance – match your shaft diameters

• □ 

  Torque: 16-5600 N·m – ensure it exceeds your requirement

• □ 

  Speed: Up to 15300 RPM – match your motor speed

• □ 

  Temperature: -35°C to +80°C – verify operating range

• □ 

  Standard: GB/T5272-2002 – quality assured

• □ 

  Application: Mining, metallurgy, pumps, fans, conveyors, textile

10. Conclusion

The ML plum blossom jaw coupling from Apex Coupling offers the perfect combination of compact design, maintenance-free operation, and high load capacity for medium-speed, medium-torque industrial applications. With 16-5600 N·m torque capacity, polyurethane spider, GB/T5272-2002 compliance, and OEM customization, it is the ideal solution for mining, metallurgy, pumps, fans, conveyors, and general industrial machinery.

👉 Need a plum blossom coupling for your application? Contact us with your model, bore, and torque requirements.